Preparation of nitrogenous fertilizer compositions



April 5, 1952 R. D. KRALOVEC ETAL 2,592,809

PREPARATION OF NITROGENOUS FERTILIZER COMPOSITIONS Filed Jan. 27, 19 49INVENTORS ROBERT D. KRALOVEO and ROBERT L. HUFFMAN AGENT Patented Apr.15, 1952 PREPARATION OF NITROGEN OU S FERTILIZER COMPOSITIONS Robert D.Kralovec and Robert L. Huffman, Wilmington, Del., assignors to E. I. duPont de Nemours & Company, Wilmington, DeL, a corporation of DelawareApplication January 27, 1949, Serial No. 73,052

1 This invention relates to the preparation of gradually-availablenitrogenous fertilizer compositions, and more particularly it relates toa.

new and useful process for preparing such compositions from urea andformaldehyde.

It has'been known heretofore that fertilizer compositions may beprepared by reacting urea with formaldehyde under certain specifiedconditions. For example, Rohner and Wood in U. S. Patent 2,415,705-describe the reaction of 0.75 to I.25 mols formaldehyde and 1 mol ureaat a pH of 3 to 5 and at temperatures within the range 40 to 75 C. togive a resin having fertilizer properties.

Urea-formaldehyde fertilizers of this general nature are potentiallyvery attractive for three reasons. They are non-hygroscopic; theycontain large amounts of nitrogen in a form which is Water insolubleandhence not easily leached from the soil; and this nitrogen is availableas plant food, but instead of all being available in the soil at aparticular time, it becomes available gradually throughout the growingseason. The need for such fertilizer materials is great because thenatural organic materials such as blood meal and tankage' which havebeen used for this purpose in the past are in short supply and command'high prices.

It is an object of this invention to provide an improved process forpreparing urea-formalda hyd'e fertilizer compositions. It is another object of this invention to provide such a process which is rapid,continuous, economical, and well adapted for commercial use. A furtherobject is to provide a process for preparing urea-formaldehydefertilizer compositions of consistently high quality as regards theinsolubility and availability of their nitrogen contents. Other objectsof the invention will appear hereinatfer.

According to this invention, it has been found that superior solidurea-formaldehyde fertilizer compositions may be obtained bycontinuously introducing aliquid aqueous composition containing from 1.3to 11.6 molecular equivalents of urea per molecular equivalent offormaldehyde onto a moving surface in an amount sufiicient to form athin layer on said. surf-ace'of' from a e inch to 1/4 inch in thickness,subjecting the unaa-formalde- 19 Claims. Cl. 260-69) outer curvedsurface of a drum or cylinder which rotateson its axis and which may beprovidedon its innerside with a heat transfer medium such as steam.

.A clearer understanding of certain features of the invention may be.had by reference to thefigures in the drawing, which, however, are-to beviewed merely as aids in explaining the proc'-- is continuously mixedwith acid catalyst intro duced at 2. This acidified composition passesthrough a short mixing'section 3 and is then distributed by a spreaderdevice 4 onto the outer curved suriace'i of the drum-reactor 6. Forease'of cleaningin the event of polymer build-up, it is axis in the directionindicated by the arrow,- and hyde composition to reaction thereon at atemmay be driven by any suitable mechanism including, for instance, thegear arrangement sub-- gestedat 8. The temperature on the drum surfaceis contrclled by means of steam of the desired pressure introduced intothe drum from pipe 9 and exhausted at the other end of the drum througha pipe not shown. As the liquid composition contacts the drum, it formsinto a thin filmwhose thickness is dependent upon the relative rates offeed introduction and rotation of the drum-reactor." As the film movesaway from 'itspoint of introduction, it rapidly begins to thickenandsolidify under the influence of the.

acid catalyst and the high temperature. After a given portion of thefilm has completed nearly afull" rotation'on the drum, the reaction isfinished. The solidified product isremove'd, as by means of the doctorknife 10', and drops into a container or hopper ll. Thereafter theproduct is preferably-cooled, the acid catalyst is neutralized, and theproduct is dried to provide a fertilizer which will retain its desirablecharac' teristics over a long period. The use of a rubher darn it may beadvantageous in forming a small. pool of the liquid composition-andpreventing its running down the wrongside' of the drum.

If a .dam is used, fresh feed should be added to the edge of the dam todisplace the reactingpool 1 dang.

The process may be modifledfif desiredl by contacting the solidifiedproduct while still on the drum with a neutralizing agent. When sooperating, the drum is generally rotated at a relatively slower speed sothat the reaction is finished after a smaller arc has been traversed. Atthis point, a neutralizing agent is either spread as a solid or sprayedas a liquid over the product by a movable mechanism such as that shownat l2. The neutralized product then remains on the drum and aconsiderable portion of its water content is evaporated away before itreaches the doctor knife Ill. I

Another embodiment of the invention is depicted in Figure 2 wherein thedrum I4 is in effect turned so that one 'end I5 is uppermost, and thatend is preferably flanged outwardly as shown at it. As in the processof, Figure 1, the acidified liquid composition is continuously fedthrough a spreading device I! and onto the surface of the rotating drum1 4 in the form of a thin film 18. After the reaction is complete, thesolidified product is removed by one or a number of doctor knives l9;The temperature is controlled by means of steam introduced into thehollow inside of drum M through pipe 26 and removed through pipe 2|. Ifit is' desired to neutralize the reaction product,'this may be doneeither after removal of the product from the drum surface or while it isstill on the drum. In the latter instance, the neutralized product mayconveniently be allowed to remain on the drum in order that it may bedried by evaporation of a portion of its water content.

Careful control of all the reaction variables is essential in order totake advantage of the rapid reaction rate of this novel process and atthe same time obtain a high quality fertilizer Prior processes haveinvolved very much longer reaction times because .the presentcombination of conditions was not known, nor was any method known forcontrolling the reaction and keeping it within these conditionsEvaluation of these urea-formaldehyde fertilizer compositions is basedmainly on two properties, their insolubility and their availability forplant nutrition The insolubility is expressed as that percentage of thetotal nitrogen content which is water-insoluble It is determinedaccording to the Official and Tentative Methods of Analysis of theAssociation of Official Agricultural Chemists, 6th ed, 1945, procedure2.35. The availability may be expressed as the percentage of theinsolublenitrogen which nitrifies during a certain period in the soiland is dependent to a certain extent upon the type of soil in which thetest is made. A reasonably accurate estimate of the-availability may beobtained by determining the percentage of the insoluble nitrogen whichdissolves when a sample of 0.25 g. of the productis heated to 100? C.for 30 minutes in 250 ml. of neutralized water. The percentage-figurethus obtained is called the availability index, and is approximatelyequal to the amount of insoluble nitrogen which nitrifies during thefirst six months in the soil. For most uses, urea-formaldehydefertilizer compositions should contain at least about 60% of theirnitrogen in an insoluble form, and at least about 50% of this insolublenitrogen should be available for plant nutrition within six months inthe soil, i. e. the availability index should be at least about 50%. Forcertain-uses, however, compositions characterized by an availabilityindex between 48 and 50% have proved very advantage'ous. a

conditions of this The mol ratio of urea to formaldehyde in the feed isone of the most important variables affecting product quality. If theremaining process variables are held constant within the preferredranges, the availability index of the product is too low when mol ratioslower than about 1.3:1 are employed and the insolubility of the productbecomes too low when mol ratios higher than about 1.611 are employed. Itis believed that the desired product may be represented by the formula:

NI-I2.CO.NH.CH2 [NI-I.CO.NH.CH2 x.NH.CO.NHz

where .:c=1 to 4, and, under the rapid reaction invention, the greatestamounts of these compounds are formed when the stipulated mol ratios ofreactants are employed. The use of the higher mol ratios is advisablesince the cost of the product is thereby decreased and its nitrogencontent is increased.

In preparing the liquid iced composition for the process of thisinvention, it is possible to mix the formaldehyde with a urea solutionimmediately before adjusting the pH and introducing the composition ontothe moving surface. It is also possible to obtain a relatively stable;premixed feed by the following means: (1) neutralizing the formaldehydeto a pH between 9.0 and 9.5 before mixing it with the urea; and, (2)heating the mixture of neutralized formaldehyde solution and urea toabout 60 C. for 20 minutes and then cooling to about 25 (3., or heatingto about 40 C. until the urea is dissolved andthen keeping it at about35 C. If it is desired to speed up the reaction onthe moving drum, thepre-mixed feed may advantageously be heated to about 60 or 70? C. priorto addition of the acid catalyst. A small amount of resinification-inthe feed may be desirable, but feed which has become more resinifiedshould be used promptly.

Either crude or crystal urea maybe employed as the raw material in theprocess. The formaldehyde may be provided in the form of the usual 37%aqueous solution, .or in the form of a concentrated aqueous solution ofabout 60% formaldehyde content, or'in the form of a solue tion of highermethylol ureas derived,- for instance, by reacting 4 to 6 mols of hot,concen-' trated formaldehyde with 1 mol of urea ata pH of 7.0 to 9.0according to the method disclosed by H. M. Kvalnes in U. S. patentapplication Ser. No. 732,927, now U. S. Patent 2,467,212. The advantageof employing these latter forms of formaldehyde is that they makepossible the preparation of more concentrated feeds which in turn speedupthe ultimate reaction andminimize subsequent product dryingrequirements. The higher methylol ureas are particularly useful in thatthey eliminate practically all loss of formaldehyde during the process.Feeds containing from 60% to solids content, i, e. from 40% to 15%water, are preferred, although good results can be obtained outside thisrange. The presence of methanol in the formaldehyde is notobjectionable. Film thicknesses in excess of about A; inch during thesolidification result in non-uniform products, the top being waxy andthe bottom plaster-like, and hence are to be avoided. The use of filmthicknesses of less than 5% inch is not injurious in itself, but itunnecessarily decreases the capacity. of the equipment without anycompensating benefits.

The relatively high temperatures empl lyfidf in the process of thisinvention constitute one of its unique features, since temperatures inthis range have hitherto-been purposely avoided. Tempora tunes. in therange of I .BOP'tQ il make .possible a veryrapid :zreaction, but-unlessthe .remaining variables are simultaneously controlled accordmg :to "the.present teachings, the :use of high :temperatures alone will result ina product havingpoormitrogen availability. At temperatures below aboutC.., the reactionproceeds'very slowlyand theadvantages of the inventionare notfully realized. Above about 120 'C,, blisteringand:splatteringofthe liquid "composition on the moving surface occurs.The insolu-bility of the product increases as the temperature .is raisedfrom to 100" -C but doesrnotincrease much as the temperature is'raisedhigher. "Hence the preferred operating temperature is within the rangeof-780 to 100 -C.

. Anacid catalyst is necessary in order-to make the reaction go and thehigher the acid concentration, the faster the reaction proceeds. -Ata.pI-I lower than about 2.0, howeverythe availability of the nitrogen inthe product is decreased inordinately. pH of about 6.0 is the upperlimit for reasonably rapid reaction. "Acids such as sulfuric,hydrochloric, phosphoric, nitric, formic 'andthelike, and acid salts.suchas sodium acid pyrophosphate have been employed interchangeably asthe catalyst. -W-hen employing sulfuric acid,-about 0.03% by weight,based'on the weightof urea plus formaldehyde in the feed, is neededto-give a pH of --6.0, and about .0% by weight isneededto :give apI-I-of 2.0. A- pH of from 3.0 to 2.5, corresponding toa-bout 0.1% .to0.25% of. sulfuric acid, is preferred.

,Thetime required for the -:r.eaotion-may vary considerably dependingupon tl-ieschoice of other conditions. action is much faster.-acc0rding-to the present processthan it is under any process knownheretofore. Increasingthe temperature, increasing the acidity,decreasing the watercontent of the Almost invariably, however, theresu'lts may also be -obtained by-employing gaseous ammonia or liquidammoniacal iso'lutions. As stated i hereinbefore, the product may be"neutralized while .still on the "drum reactor, for instance, or after"removal therefrom. The advantage of neutralization is thatiit preservesthe availability characteristics of the fertilizer.

:Anyrmovingsurface such as that .offaro'tatzingidrum, a rotating "disk,2. continuous beltor the like,1may.;be employed in the process of thisinvention. The preferred apparatuszcomprises a .h'ollow drum adapted tohave 11a heat control :medium passed through it, :as 'shownin the "fig--uresofthe drawing. .It .is alsoipossible 'to'employ two drums mountedside'iby :side with-their axes running "parallel to each other in ahorizontal plane. Asmall pool of liquid ismaintained above the pointofcontact 'oftthe .two drums and asrthe drums rotate in oppositedirections upwardly and away. from this point, film fare formed "andcar- .ried upwardly with the-drums. Eithersteam or hotiwater is "the'mo'stsuitable heat control medium, the'temperature of thesteam, ofcourse,

being regulated. by means ofthe amount of presfeed, decreasing themolratio of urea to formaldehyde, .and decreasing the thickness of thelayer on the moving surf-ace all have theeffect ofdecreasing thereaction time, and alltend to reduce the availability of .theinsolubienitrogen in the product. The reaction should be allowed to .continueuntil solidification occurs and the product can be scrapedfrom themoving surface. If the product is allowed to remainunneutralized fortoolong on the heated moving surface, its insolubility will increase butits availability will soon drop below the desired level. Reaction times:of from 10 to 200 seconds-have been employed forthe most part, butshorter or longer times may also be employed satisfactorily. Re actiontimes of from 10 to 60 seconds are'preferred from the standpoint ofobtaining higher a stoichiometric amount or an excess of perhaps Forexample, undried flakes as scraped from the drum reactor may be tumbledwith calcium carbonate-powder followed bydrying, or,

the dried ground productmay be mixed with an excess of powdered calciumcarbonate followed by water spraying. and drying. Excellent .re-

sure or vacuum under-whichit is employed. The surface itselfi'n'aycomprise any "relatively hard material which is unaffected by thereactants and the temperature. Acid-resistant: metals I'Sll'Ch asstainless steel, chromium 'or :nickel-i plated metals, acid-resistanthard plastics, hardened rubber-like compositions, etc. are all useful.Thev particular "design features and the dimensions of the dru-m orother moving "surface will .be apparentwto those skilled in the-art.

'E.rampZe;1.-"A 36% :aqueous solution of substantially 31116151181101sfree formaldehyde was treated -withan aqueous solution ofsodium-hydroxide tab-ring the .pH to about 9. About/1.5 mols of crystalurea was added per mol 'of formaldehyde and the solutiongradually-heated to C. where it waskeptfor 20 minutes. The solution wasthen allowedto cool-and "the .pH checked toinsure that it was above 7.This feed solution was continuously mixed with 10% aqueous sulfuric-acidloan amount sufficient to bring the pH to 3:0, as measured by diluting10 cc. of feed withil) cc. of water. After passing through a shortmixing trough, the liquid feed was spread onto a "chromium-platedstainless steel drum 14 inches in diameter, .12 inches wide,and-generallysimilar tothatshown inFigure 1. The drum surface was keptat about80 to 90C. by steam introduced under aslight vacuum, and thedrum wasrotated-at 1 R. P. M. The film thickness on the .drumaveragedapproximately ale inch. The product was easily fiaked'from the drumafter 85% of therotation .had been-com pleted. which represented a timeon the drum of 50 seconds. The product was neutralized by tumbling withfrom 0.5 to 1.0% by Weight-of powdered calcium carbonate and a smallamount, lessthan-l0% by weight, of water. It wasthen dried and crushedto givea granular free-flowing fertilizer having a totalnitrogenconten-tof 405%, an insoluble nitrogen content of 61.5% of the.total nitrogen, and an availability index of 60%.

Example .2.-About 94 pounds.of 236.2%}01111- aldehyde solution(substantially methanol-free) was treated with 113 cc. of 6 N sodiumhydroxide solution to bring its -pH-to 9.3. 102 pounds of crystal ureawas added to the formaldehyde in a jacketed glass-lined kettle withagitation and the mixtureheated toabout 60 C. Afterbeinggheld at 260(3.. for emu-too minutes. the solution "was.

cooled to about C. Its pH was 9.9. The above feed was pumped into amixing trough at a rate of approximately 52 lbs/hour and 9.6 weight percent sulfuric acid solution added at a rate of 369 gms./hour. The pH ofthe mixture, after acid addition was 3.0 (mixture diluted 4 to 1 withdistilled water for pH measurement). The liquid mixture was fed onto thetop of a chromium-plated stainless steel drum 14 inches in diameter, 12inches wide, and generally similar to that shown in Figure 1. The drumsurface was kept at 100 C. by atmospheric steam, and the drum wasrotated at 2 R. P. M. The product was easily flaked from the drum after85% of the rotation had been completed, which represented a time on thedrum of about 25 seconds. 102 lbs. of product containing 27.9% water wascollected. This product was neutralized, dried and crushed as follows:85 lbs. of the undried product was tumbled with 386 gm. of powderedcalcium carbonate for 1 hour. Then about 7 lbs. of water was sprayedinto the mixture while tumbling and tumbling continued for 20 minutes.The fairly free-flowing fiakes were then discharged into trays and driedwith 180 to 225 F. air for 8 hours. The dried product was then crushedthrough a 20 mesh screen on an oscillating granulator. The pH of theproduct before neutralization was 2.8 and after neutralization 7.8. Thedried product contained total nitrogen. Its insoluble nitrogen contentwas 29.0% or 72.5% of the total nitrogen and its availability index was18%.

The advantage of the present process is that it makes possible theaccurate control of the several critical conditions which have beendiscovered. As a result, urea-formaldehyde fertilizer compositions whichare of consistently high quality may be prepared with surprisingrapidity on a practical commercial scale.

The products obtained by the process of this invention can be mixed withmany other types of fertilizers in order to obtain balanced compositionscontaining phosphorus, potassium, and the like. They may also be mixedwith other nitrogen-containing fertilizer ingredients including urea,ammonium sulfate, ammonium nitrate, ammoniating solutions, etc. Aparticularly useful effect is observed when the urea-formaldehydeproducts are mixed with fertilizer constituents containing free urea,such as urea-ammonia liquors, because the free urea exercises astabilizing action on the urea-formaldehyde which is not observed uponmixing with the nitrate liquors or other comparable products. Thisstabilizing action is most noticeable at the higher temperaturesencountered during curing and pile storage.

Since many changes and modifications of the process of this inventionwill occur to those skilled in the art, it is not intended that theinvention should be limited in any way other than by the followingclaims.

We claim:

1. A method for preparing a solid urea-formaldehyde fertilizercomposition which comprises continuously introducing a liquid aqueouscomposition containing from 1.3 to 1.6 molecular equivalents of urea permolecular equivalent of formaldehyde onto a moving surface in an amountsufficient to form a thin layer on said surface of from inch to A; inchin thickness, subjecting the urea-formaldehyde composition to reactionthereon at a temperature of from 60 to: 120 C. and at a pH of from 2 to6 until solidi- 8 fication of the composition occurs, and thereaftercontinuously removing the solidified product from said surface.

2. A method for preparing a solid urea-formaldehyde fertilizercomposition which comprises continuously introducing a liquid aqueouscomposition containing from 1.3 to 1.6 molecular equivalents of urea permolecular equivalent of formaldehyde onto the outer surface of aslowlyrotating drum in an amount sufficient to form a thin layer thereonof from inch to $4; inch in thickness, subjecting the urea-formaldehydecomposition to reaction on the drum at a temperature of from 60 to 120C. and at a pH of from 2 to 6 until solidification of the compositionoccurs, and thereafter removing the solidilied product before any givenportion of the reactants has made a complete rotation on the drum.

3. A method for preparing a solid urea-formaldehyde fertilizercomposition which comprises preparing an aqueous urea-formaldehydesolution having a pH of from 9.0 to 9.5, a solids content of from 60% to85%, and a ratio of from 1.3 to 1.6 molecular equivalents of urea permolecular equivalent of formaldehyde; heating said aqueous solution to atemperature of from 50 to C.; adding an acidic catalyst to this heatedsolution to produce a pH of from 2 t0 6; promptly introducing thisacidified solution onto the outer surface of a slowly-rotating drum inan amount sufficient to form a thin layer thereon of from inch to inchin thickness; subjecting the urea-formaldehyde composition to reactionon the drum at a temperature of from to 100 C. and at a pH of from 2 to6 until solidification of the composition occurs; and thereafterremoving the solidified product before any given portion of thereactants has made a complete rotation on the drum.

4. A method for preparing a solid urea-formaldehyde fertilizercomposition which comprises preparing a liquid aqueous compositioncontaining from 1.3 to 1.6 molecular equivalents of urea per molecularequivalent of formaldehyde and containing from about 60% to aboutsolids, continuously introducing said aqueous composition onto the outercurved surface of a slowlyrotating drum in an amount sufiicient to forma thin layer thereon of from 3 2' inch to A inch in thickness,subjecting the urea-formaldehyde composition to reaction on the drum ata temperature of from 80 to C., at a pH of from 2 to 6, and during atime interval of from 10 to 200 seconds, whereby solidification-of thecomposition occurs, and thereafter removing the solidified productbefore any given portion of the reactants has made a complete rotationon the drum, the temperature of the reactants on the drum beingcontrolled by means of steam introduced into the inside of the drum.

5. A method for preparing a solid urea-formaldehyde fertilizercomposition which comprises preparing a liquid aqueous compositioncontaining from 1.3 to 1.6 molecular equivalents of urea per molecularequivalent of formaldehyde and containing from about 60% to about 85%solids, continuously introducing said aqueous composition onto the outersurface of a slowly-rotating drum in an amount sufiicient to form a thinlayer thereon of from inch to 4 inch in thickness, subjecting theurea-formaldehyde composition to reaction on the drum at a temperatureof from 60 to C. and at a pH of from 2 to 6 until solidification of thecomposition occurs,

greases.

treating the solidified composition While on the drum with at least theamount of base required to react stoichiometrically with all of the acidpresent, maintaining the neutralized compositiononthe drum at atemperature of from 60 to 120 C. for a short time to effect a partialdrying thereof, and thereafter removing the solidified. product beforeany given 'portion of the reactants has made a complete rotation on thedrum.

6. A method for preparing a solid'urea-f'ormaldehyde fertilizercomposition which comprises continuously introducing a liquid aqueouscomposition containing from 1.3 to 1.6 molecular equivalents of urea permolecular equivalent of: formaldehyde onto a moving surface in anamount: sufficient to form a thin layer on said surface of from 3 2 inchto 4 inch in thickness, subjecting the urea-formaldehyde compositiontoreaction thereon at a temperature of from 60 to 120 C. and at a pH offrom 2 to 6 until solidification ofthe' composition occurs, andthereafter neutralizing the resulting urea-formaldehyde com-- position.1

7. A method for-preparing a solid urea-formaldehyde fertilizercomposition which comprises preparing a liquid aqueous compositioncontaining from 1.3 to 1.6 molecular equivalentsof urea: per molecularequivalent of formaldehyde andcontaining from about 60% to about 85%solids, continuously introducing said aqueous composi-= tion onto amoving surface in'an amount suffi cient. to form a thin layer 'on saidsurface of from 1%; inch to inch in thickness, subjecting the.urea-formaldehyde composition to reaction thereon at a temperature offrom 60 to120- C. and at a pH of from 2 to 6 until solidification ofthecomposi-tion occurs, continuously removing the solidified productfrom said surface and thereafter neutralizing the resultingurea-formaldehyde composition.

8; A method for preparing a solid urea-formaldehyde fertilizercomposition; which comprises. preparing a liquid aqueous compositioncontaining from 1.3 to 1.6 molecular equivalents of urea per molecularequivalent of formaldehyde and containing from about 60% to about 85solids, continuously introducing said aqueous composition onto a movingsurface in an amount sufficient to form a thin layer on said surface, offrom 3? inch to inch in thickness, subjecting the urea-formaldehydecomposition to-reaction thereon at a temperatureiofifrom. 60to 120 C.and at a pH of from 2 to 6 until solidification of the.- compositionoccurs, neutralizing the resulting urea-formaldehyde composition whilestill on said surface, and thereafter continuously removing thesolidified product from said surface.

9. Amethod for preparinga solid:urea-formal, dehyde fertilizercomposition which comprises; continuously introducing a liquid aqueouscomposition containing from 1.3 to 1.6 molecular equivalents of urea permolecular equivalent of formaldehyde onto a heated surface in an amountsufficient to form a thin layer on said surface of from 3 2' inch toinch in thickness, subjecting the urea-formaldehyde composition toreaction thereon at a temperature of from 60 to 120 C. and at a pH offrom 2 to 6 until solidification of the composition occurs, andthereafter continuously removing the solidified product from saidsurface.

10. A method for preparing a solid urea-formaldehyde fertilizercomposition which comprises preparing a liquid aqueous compositioncontaining from 1.3 to 1.6 molecular equivalents of urea the stepsofadding'urea'to a formaldehyde solutionhaving. apH of from 90 to 9.5toproduce an aqueous solution having a solids content of" from abouttoabout 85%, and-a ratio of from 1 .3 to l'.5 mol'ecular equivalentsofurea per per molecular equivalent of formaldehyde and tion to reactionon said surface at a temperature of from 60 to 120 C. and at a pH offrom 2 to 6 until solidification of'the composition occurs, andthereafter continuously removing the solidified productv from saidsurface.

11. Amethodfor preparing a solid urea-formaldehyde fertilizercomposition which comprises preparing an aqueous urea-formaldehydesolution having apH of from 9.0-to9.5, a solids content of'60 to and aratio-of from 1.3 to 1.6. molecular equivalents of urea permolecularequivalent: of formaldehyde; heating said aque-' ous solutionto atemperature of from 50 130 75 C.;. cooling the solution to below- 400.; adding an acidic catalyst to this solution to produce a pH of from 2to 6; promptly introducing this acidified solution onto the outersurface of a slowlyf-rotating drum" in an amount sufi'icient to. form.a. thin-layer: thereon of from 2 inch'to 4. inch in thickness;subjecting the urea-formal dehyde composition to reaction on the drumata temperature of from 80 to C. and at av pHof'. from 2 to 6 until:solidificationof the-composition occurs; and thereafter removing thesolidified product before any given portion of the" reactants hasrmad'e'a .complete rotation o the 12.. A method for preparing a solid.urea-formaldehyde: fertilizer composition which comprisespreparing anaqueous: urea-formaldehyde" solutionihaying apH greater. than 7.0, asolids content1of from about-60 to about 85% and a. ratio of from .1.3to 1.6-molecularequivalents of urea per molecular equivalent offormaldehyde; acidifying; continuously introducing the acidifiedsolution onto amoving surface in an amount sufficient toform a. thinlayer on said surface of from 1:5 inch to inch in thickness, subjectingthe. urea-formaldehyde composition to reaction thereonat a; temperatureof from 60 to-.120 'C.:

and atza. pH of from 2 tosfifuntil solidification of the. compositionoccurs, and: thereafter continuously removing. the solidified productfrom said v surface.

13. Al method' for preparing a solid urea-formaldehyde fertilizercomposition which comprises molecular equivalent of formaldehyde;acidifying; continuously introducing the acidified solution onto amoving surface in an amount sufficient to form a thin layer on saidsurface of from inch to inch in thickness, subjecting theurea-formaldehyde composition to reaction thereon at a temperature offrom 60 to C. and at a pH of from 2 to 6 until solidification of thecomposition occurs, and thereafter continuously removing the solidifiedproduct from said surface.

14. A method for preparing a. solid urea-formaldehyde fertilizercomposition which comprises preparing an aqueous urea-formaldehydesolution having a pH greater than 7.0, a solids con- 1 1 tent of fromabout 60% to about 85% and a ratio of from 1.3 to 1.6 molecularequivalents of urea per molecular equivalent of formaldehyde; reactingthe urea and formaldehyde on a moving surface in the form of a thinlayer of from inch to ,4; inch in thickness at a temperature of from 60to 120 C. and at a .pH of from 2 to 6 until solidification of thecomposition occurs; and thereafter continuously removing the solidifiedproduct from said surface.

15. A method for preparing a solid urea-formaldehyde fertilizercomposition which comprises the steps of adding urea to a formaldehydesolution having a pH of from 9.0 to 9.5 to produce an aqueous solutionhaving a solids content of from about 60% to about 85%, and a ratio offrom 1.3 to 1.6 molecular equivalents of urea per molecular equivalentof formaldehyde; heating said aqeous solution to a temperature of from50 to 75 C.; cooling the solution to below 40 C. maintaining; the cooledsolution at a pH greater than 7.0; acidifying; continuously introducingthe acidified solution onto a moving surface in an amount sufficient toform a thin layer on said surface of from 3 inch to inch in thickness,subjecting the urea-formaldehyde composition to reaction thereon at atemperature of from 60 to 120 C. and at a pH of from 2 to 6 untilsolidification of the composition occurs, and thereafter continuouslyremoving the solidified product from said surface.

16. A method for preparing a solid urea-formaldehyde fertilizercomposition which comprises preparing a liquid aqueous compositioncontaining from 1.3 to 1.6 molecular equivalents of urea per molecularequivalent of formaldehydeand containing from about 60% to about 85%solids, continuously introducing said aqueous composition onto a movingsurface in an amount sufficient to form a thin layer on said surface offrom 3 inch to A; inch in thickness, subjecting the urea-formaldehydecomposition to reaction thereon at a temperature of from 60 to 120 C.and at a pH of from 2 to 6 until solidification of the compositionoccurs, and thereafter continuously removing the solidified product fromsaid surface.

17. A method for preparing a solid urea-formaldehyde fertilizercomposition which comprises preparing a liquid aqueous compositioncontaining from 1.3 to 1.6 molecular equivalents of urea per molecularequivalent of formaldehyde, and containing from about 60% to about 85%solids, continuously introducing said aqueous composition onto the outersurface of a slowly rotatin drum in an amount suflicient to form a thinlayer thereon of from i inch to A inch in thickness, subjecting theurea-formaldehyde composition to reaction on the drum at a temperatureof from 60 to 120 C. and at a pH of from 2 12 to 6 until solidificationof the composition occurs, and thereafter removing the solidifiedproduct before any given portion of the reactants has made a completerotation on the drum.

18. A method for preparing a solid urea-formaldehyde fertilizercomposition which comprises preparing a liquid aqueous compositioncontaining from 1.3 to 1.6 molecular equivalents of urea per molecularequivalent of formaldehyde and containing from about to about solids,continuously introducing said aqueous composition onto a moving surfaceinan'amount sufficient to form a thin layer on said surface of from inchto 3 inch in thickness, subjecting the urea-formaldehyde composition toreaction thereon at a temperature of from 60 to C. and at a pH of from 2to 6 until solidification of the composition occurs, and thereafterneutralizing the resulting ureaformaldehyde composition.

19. A method for preparing a solid urea-formaldehyde fertilizercomposition which comprises preparing a liquid aqueous compositioncontaining from 1.3 to 1.6 molecular equivalents of urea per molecularequivalent of formaldehyde and containing from about 60% to about 85%solids, continuously introducing said aqueous composition onto a heatedsurface in anflamount sufficient to form a thin layer on said surface offrom 3*; inch to inch in thickness, subjecting the urea-formaldehydecomposition to reaction thereon at a temperature of from '60 to 120 C.and at a pH of from 2 to 6 until solidification of the compositionoccurs, and thereafter continuously removing the solidified product fromsaid surface.

ROBERT D. KRALOVEC. ROBERT L. HUFFMAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,929,624 Canon Oct. 10, 19332,034,599 Van Marie Mar. 17, 1936 2,118,439 Lawrence et a1. May 24, 19382,345,013 Soday Mar. 28, 1944 2,415,705 Rohner et a1." Feb. 11, 19472,456,192 Houlton Dec. 14, 1948 FOREIGN PATENTS Number Country Date419,422 Canada Apr. 4, 1944 OTHER REFERENCES Clark et al., A Slow-ActingNitrogen Fertilizer, Chemical Trade Journal and Chemical Engineer,August 6, 1948. pages 149-150.

1. A METHOD FOR PREPARING A SOLID UREA-FORMALDEHYDE FERTILIZERCOMPOSITION WHICH COMPRISES CONTINUOUSLY INTRODUCING A LIQUID AQUEOUSCOMPOSITION CONTAINING FROM 1.3 TO 1.6 MOLECULAR EQUIVALENTS OF UREA PERMOLECULAR EQUIVALENT OF FORMALDEHYDE ONTO A MOVING SURFACE IN AN AMOUNTSUFFICIENT TO FORM A THIN LAYER ON SAID SURFACE OF FROM 1/32 INCH TO 1/4INCH IN THICKNESS, SUBJECTING THE UREA-FORMALDEHYDE COMPOSITON TOREACTION THEREON AT A TEMPERATURE OF FROM 60* TO 120* C. AND AT A PH OFFROM 2 TO 6 UNTIL SOLIDIFICATION OF THE COMPOSITION OCCURS, ANDTHEREAFTER CONTINUOUSLY REMOVING THE SOLIDIFIED PRODUCT FROM SAIDSURFACE.